In the related art, it is necessary to identify a user in order to permit the user to use some or all of functions of personal information terminal equipment (hereinafter, referred to as a ‘terminal’) such as a mobile phone.
In many cases, the following method has been used frequently: an input character string pattern called a code number or a password, which is secret information of an authorized user, is determined beforehand; and only when the determined character string pattern is input, the user will be authenticated.
However, in the user authentication using such secret information, when the terminal falls into another's hands, another person can find a correct PIN by guessing the PIN from the birthday of the authorized user, stealing a glance at the input of the password by the authorized user, or randomly inputting the various PIN, and then input the found string pattern to use the terminal. Therefore, as more secure and convenient authenticating method, user authentication using the user's biometrics has been used.
In an example of authentication method using biometric features, such as a face of an authenticated user, a face pattern of an authorized user is captured by a camera of a terminal beforehand, and then registered in the terminal. At user authentication, the face of the user who attempts to use the terminal is captured by the camera. When similarity between the captured face image and the registered face image is sufficiently high, the user is determined as an authorized user, and the user authentication succeeds.
As an authentication method by matching between face images, a so-called EigenFace method (refer to Non-patent Document 1) has been known. In the EigenFace method disclosed in Non-patent Document 1, the size of each image in a set of images is normalized, and a partial space of a feature vector composed of gray values of pixels in each image is generated by a principal component analysis. In addition, the feature vectors of an input image and of a registered image are projected onto a partial space to calculate a matching score. Then, user authentication is performed on the basis of the calculated matching score.
In the above mentioned method, an appropriate face matching method is used to sufficiently suppress a risk of pretending in user authentication, and can solve the problem of the password method that has been generally used in the related art, that is, the problem that an unauthorized user can find the password by guess or stealthy glance.
Non-patent Document 1: M. Turk, A. Pentland, “Eigenfaces for recognition”, Journal of Cognitive Neuroscience, Vol. 3, No. 1, pp. 71-86, 1991.